Indeed, airplane jet engines generate significant noise pollution. There is a high demand for reducing this pollution, even more so given that the jet engines used are becoming increasingly powerful. The design of the nacelle surrounding the jet engine contributes in large part to the reduction of that noise pollution.
In order to further improve the acoustic performance of aircrafts, the nacelles are provided with acoustic panels aiming to attenuate the noise due to the circulation of flows of air through the jet engine as well as the vibrations of the structures of the nacelle.
The acoustic panels are of the sandwich-type structure well known for absorbing that noise. These panels usually include one or several layers of structures with a cellular core (structure commonly called “honeycomb”). The layers can then be coated on their so-called outer face, i.e. the face radially farthest from the axis of the engine, with an air-impermeable skin, called “full”, and on their inner face, i.e. that radially closest to the axis of the engine, with an air-permeable perforated skin, called “acoustic”.
In a known manner, the cellular core structure is realized from joined cellular units having cells of generally hexagonal or elliptical shape.
The acoustic properties of the acoustic panel, i.e. its noise absorption rate depending on the frequency and noise level of the noise, depend in particular on the junction of the cellular unit(s).
The joining of the lateral ends is commonly done using a foaming glue, such as AFM 410® glue, which has a significant capacity for expansion. The adjacent edges of the cellular unit(s) are coated with glue which, during its expansion, obstructs the cells by creating oversizes. These oversizes have the drawback of decreasing the effective acoustic surface of the cellular structure and also causing brutal impedance ruptures that contribute to decreasing the acoustic performance of the acoustic panel during the operation of the jet engine.
Moreover, prior to their assembly, the cellular panels are cut to the required dimensions.
This cutting operation created a junction edge where the cells can be crushed and destroyed, which further decreases the final acoustic performance.
It will also be noted that after the cutting operation, the junction edges obtained have remains of cellular walls protruding from the junction edge and which will disrupt the thickness of the assembly zone.
It is also known to join, edge to edge, several cellular units by opening the cells situated on the edges designed to be joined and to overlap the cells as well as openings one in the other.
However, the implementation of such a structure with a cellular core is not suitable for a structure with cellular core including only one cellular unit. Moreover, this implementation is complex.